It is intended to provide a remedy and a diagnostic for a brain disease typifiedby cerebral infarction. Namely, a remedy for a mitochondrial dysfunction braindisease characterized by comprising a combination of (A) a δ-aminolevulinicacid represented by the following general formula (1), its derivative or a saltthereof with (B) an iron compound: RRNCHCOCHCHCOR(1) wherein R and R independently represent each a hydrogenatom or an alkyl, acyl, alkoxycarbonyl, aryl or aralkyl group; and Rrepresents a hydroxy, alkoxy, acyloxy, alkoxycarbonyloxy, aryloxy, aralkyloxyor amino group.